Sex differences in systemic and central morphine analgesia in rats: Organizational-activational gonadal hormone interactions and roles of gonadal hormone accumulating nuclei
Item
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Title
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Sex differences in systemic and central morphine analgesia in rats: Organizational-activational gonadal hormone interactions and roles of gonadal hormone accumulating nuclei
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Identifier
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d_2009_2013:2abe16e33622:10558
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identifier
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10743
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Creator
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Cataldo, Giuseppe,
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Contributor
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Richard J. Bodnar
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Date
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2010
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Language
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English
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Publisher
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City University of New York.
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Subject
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Experimental psychology | Behavioral psychology | Activational Effects | Adult Gonadectomy | Analgesic Sex Differences | Organizational Effects | Ovariectomy
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Abstract
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Sex differences in morphine analgesia are commonly seen following systemic and intracerebral administration with male rats displaying greater analgesic magnitudes and potencies than females. The purpose of this dissertation research was to elucidate further possible neural mechanisms which elicit these differences. Due to its common roles in both antinociceptive and reproductive behaviors, we hypothesized that the ventrolateral periaqueductal gray (vlPAG) is subject to sex differences upon morphine analgesia sensitive to organizational-activational manipulations of gonadal hormones as well as lesions of hypothalamic estradiol-containing nuclei. Thus, the first experiment examined the organizational manipulation of gonadal hormones and effects of adult ovariectomy or estradiol replacement and systemic morphine analgesia. To assess the generalizability of these effects, the second experiment evaluated these differences upon morphine analgesia elicited from the vlPAG as well as the interaction between organizational and activational gonadal hormone manipulations. The third experiment then evaluated the ventromedial hypothalamus (VMH) and the medial preoptic area (MPOA) hypothalamic estradiol-containing nuclei's contribution to and their possible role by which female rats display a smaller opiate analgesic effect.;Adult ovariectomy minimally affected morphine analgesia in neonatal vehicle-treated females, while significantly reducing the magnitude but not the potency of morphine analgesia in neonatal androgenized female rats. This suggests a limited organizational-activational gonadal hormone interaction in the mediation of systemic morphine analgesia in female rats. In marked contrast, neonatal androgenized female rats displayed significantly greater magnitudes of vlPAG morphine analgesia than neonatal vehicle-treated female rats. Adult ovariectomy significantly enhanced the magnitude and potency of vlPAG morphine analgesia in female rats treated neonatally with either vehicle or testosterone with the latter effect suggesting a strong organizational-activational gonadal hormone interaction in the mediation of vlPAG morphine analgesia in female rats.;Lesions of the VMH and MPOA strongly suggest that they act to tonically inhibit endogenous pain-inhibitory circuits in the female, but not male brain, and that removal of circulating gonadal hormones by ovariectomy and/or excitotoxic destruction of these estrogen receptor accumulating nuclei disinhibit the female analgesic response to systemic morphine. Collectively, these results strongly implicate the vlPAG, organizational and activational effects of gonadal hormones as well as hypothalamic estradiol-containing nuclei in mediating sex differences in morphine analgesia in rats.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Psychology
